MCB3020 Chapter 38 Human Diseases Caused by Viruses and Prions PDF

38 Human Diseases Caused by Viruses and Prions 1 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display. Airborne Diseases When human is source, airborne viruses are propelled from respiratory tract by coughing, sneezing, or vocalizing 2 Chickenpox (V...

38 Human Diseases Caused by Viruses and Prions 1 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display. Airborne Diseases When human is source, airborne viruses are propelled from respiratory tract by coughing, sneezing, or vocalizing 2 Chickenpox (Varicella) and Shingles (Herpes Zoster) DNA virus, member of Herpesviridae Humans serve as reservoir and source Acquired by droplet inhalation into respiratory system Chickenpox – results from initial infection – vaccine prevents or shortens illness 3 Chickenpox (Varicella) and Shingles (Herpes Zoster) Shingles (herpes zoster; postherpetic neuralgia) – reactivated form of chickenpox virus resides in cranial and sensory neurons reactivation - virus migrates down neuron Treatment – supportive; acyclovir and others 4 Measles (Rubeola) Measles – rash caused by measles virus (RNA virus) – enters body through respiratory tract Subacute sclerosing panencephalitis – rare progressive degeneration of central nervous system caused by measles virus Treatment, prevention, and control – symptomatic/supportive therapy – attenuated MMR vaccine (measles, mumps, rubella) 5 6 Rubella (German Measles) Enveloped RNA virus Mild brief rash acquired from respiratory droplets Congenital rubella syndrome – disastrous disease in the first trimester of pregnancy – can lead to fetal death, premature delivery, or congenital defects Attenuated vaccine reduced cases to 1000 and 10 congenital rubella cases per year 7 Smallpox (Variola) Caused by variola virus – large, brick-shaped complex virus – linear dsDNA Transmitted by aerosol or contact – humans are the only natural host 8 Clinical Forms of Smallpox Once highly prevalent – no longer in human populations – potential bioterrorism agent Variola major – most common, severe form – extensive rash and higher fever – 33% fatality rate Variola minor – less common form and less severe – fatality rates of 1% or less Both forms usually transmitted by direct and fairly prolonged face-to-face contact 9 Eradication of Smallpox 1977 – last case from a natural infection occurred in Somalia Why eradication was possible – – disease has obvious clinical features – humans are only hosts and reservoirs – there are no asymptomatic carriers – short infectivity period (3–4 weeks) 10 Protection from Smallpox Obtained from vaccination – use vaccinia virus in a live virus vaccine Routine immunization no longer done in the U.S. Use of vaccine is controversial because of its unknown efficacy in the prevention of bioterrorism and potential side effects Food and Drug Administration has not approved any treatment for smallpox 11 Question 2 Women of childbearing age should be vaccinated against measles (Rubeola) and German measles (Rubella) to prevent fetal death or other birth defects. True or False 12 Arthropod-Borne Diseases Arboviruses – viruses transmitted by bloodsucking arthropods from one vertebrate host to another – multiply in tissues of vector without producing disease vector acquires a lifelong infection 13 Clinical Syndromes Arboviral disease syndromes can be placed into three subsets – Undifferentiated fevers, with or without rash – Encephalitis inflammation of the brain fatality rate is usually high – Hemorrhagic fevers frequently severe and fatal Supportive treatment, no vaccines available 14 West Nile Fever (Encephalitis) Caused by a flavivirus, RNA virus Appeared in New York in 1999 causing human and animal deaths By 2006 found in all continental U.S. states, infecting humans or animals Transmitted to humans by Culex spp., mosquitoes that feed on sparrows and crows 15 West Nile Fever Human to human spread has occurred through blood and organ donation Only one antigen type exists and immunity is presumed to be permanent Clinical manifestations – fever, lymphadenopathy, rash – >1/100 patients develop serious complications (e.g., encephalitis) Treatment, prevention, and control – serology tests – supportive treatment – mosquito control measures 16 17 Direct Contact Diseases Transmission of disease through direct personal contact – touching, kissing, sexual contact, contact with body fluids, contact with open wounds – many diseases including AIDS 18 Genital Herpes Usually caused by herpes simplex type 2 – linear dsDNA – enveloped virus Very common sexually transmitted disease and to infant during vaginal delivery (congenital or neonatal herpes) Active and latent disease with reactivations 19 Genital Herpes Clinical manifestations – fever, burning sensation, genital soreness, and blisters in infected area – blisters heal spontaneously, but virus remains latent and is periodically reactivated Can be treated with antiviral drugs (e.g., acyclovir) 20 Genital Herpes Congenital (neonatal) herpes – usually HSV-2 – one of the most life-threatening of all infections in newborns – ~1,500–2,200 babies/year in U.S. – can result in neurologic involvement and blindness – Caesarian section recommended 21 Human Herpesvirus 6 Infections HHV-6 – enveloped with icosahedral capsid – dsDNA – tropism is wide, including CD8+, CD4+, natural killer, and epithelial cells – proviral DNA in human chromosomes Probably transmitted in saliva 22 HHV-6 Infections Clinical manifestations – exanthem subitum short-lived disease of infants high fever for 3 to 4 days, followed by macular rash – pneumonitis in immunocompromised individuals – implicated in chronic fatigue syndrome, lymphadenitis, and multiple sclerosis in immunocompetent adults No treatment or prevention measures 23 Warts Verrucae - horny projections on skin associated with human papillomaviruses – DNA virus, Papillomaviridae family – more than 100 different strains – infect epithelium and mucus membranes – benign epithelial tumors and cancers 24 Warts Four major types – plantar warts – verrucae vulgaris – flat or plane warts – anogenital condylomata (genital warts) Direct contact and autoinoculation Treatment – physical destruction, topical application of drug podophyllum, or injection of IFN-α 25 Genital Warts (Anogenital Condylomata) Very common sexually transmitted HPV – 1–6 month incubation period – warts, usually multiple, found on external genitalia, in vagina, or cervix or in rectum – most infections clear spontaneous Specific types of HPV cause at least 90% of cervical cancers Vaccine available against HPV 16 and 18 (responsible for causing ~80% of cervical cancers) 26 Gastroenteritis (Viral) Acute viral gastroenteritis – inflammation of stomach or intestines – important disease of infants and children – leading cause of childhood death in developing countries – probably spread by fecal-oral route Caused by four major groups of viruses 27 Gastroenteritis (Viral) Rotavirus, adenovirus, and astrovirus – ~5–10 million deaths/year worldwide – viral diarrhea transmitted by fecal oral route – rotavirus live oral vaccines Norovirus – ~23 million cases of acute gastroenteritis per year – usually self-limited disease – symptomatic/supportive therapy 28 Zoonotic Diseases Human viral infections in animal reservoirs before transmission to and between humans RNA viruses, many are on Select Agents list as potential bioweapons – Ebola and Marburg viruses – hantaviruses – Lassa fever virus – Nipah virus 29 Ebola and Marburg Hemorrhagic Fevers Viral hemorrhagic fever (VHF) – severe multisystem syndrome caused by many distinct viruses – overall host vascular system is damaged leading to vascular leaking (hemorrhage) and dysfunction (coagulopathy) 30 Ebola Hemorrhagic Fever Member of single-stranded, negative sense RNA family called the Filoviridae Infection is severe and ~80% fatal No known carrier state; fruit bat may be reservoir Transmission from direct contact with Ebola victim, body fluids or clinical samples Internal hemorrhaging Supportive therapy; no treatment available Experimental vaccines being evaluated 31 Prion Diseases Transmissible spongiform encephalopathies – fatal neurogenerative disorders caused by prions – remains clinically silent for months or years – ends in profound disability or death Diseases include – Kuru, Creutzfeldt-Jacob (CJD) disease, and variant CJD, bovine spongiform encephalopathy (BSE) Transmission – medical procedures, genetic, food-borne 32 Prion Diseases Prions (protein infectious particles) consist of abnormally folded proteins (PrPsc) which can induce normal forms of protein PrPc to abnormally fold BSE agent survives gastrointestinal tract passage, and is neurotropic, both serve as source of agent 33 Prion Diseases Dementia is primary symptom Usually accompanied by motor dysfunction Symptoms appear after prolonged incubation and last from months to years prior to death Produce characteristic spongiform degeneration of brain and deposition of amyloid plaques Share many characteristics with Alzheimer’s disease 34 New-Variant CJD Transmitted from cattle with bovine spongiform encephalopathy (BSE) or mad cow disease Cattle experimentally infected with BSE test positive for prion agent – evidence suggests human vCJD may be acquired by eating meat products (brain and spinal cord tissue) from infected cattle 35 36